1. Technical Field
The disclosure relates to a magnetic field detection device for detecting weak magnetic fields.
2. Related Art
There is known a position measurement technique for measuring a position of a detection target by detecting a weak magnetic field generated by the detection target. For example, in the field of endoscope, there has been developed a position detecting system for measuring a position of a capsule endoscope inside a subject by attaching a marker coil for generating an alternating magnetic field to the inside of a capsule endoscope that can be introduced into an alimentary tract of a subject, and by detecting the alternating magnetic field generated by the marker coil by a magnetic field detection device that is provided outside the subject.
According to such a position detecting system, since the strength of the alternating magnetic field that is generated by the marker coil is weak, the signal detection sensitivity (the S/N ratio of a detection signal) of the magnetic field detection device has to be increased in order to increase the accuracy of position detection for the capsule endoscope.
As examples of high-sensitivity magnetic field detection device, there are known a SQUID fluxmeter that uses a superconducting quantum interference effect, a GMR magnetic sensor that uses a giant magneto resistive effect, and the like. These magnetic field detection devices use self-excitation to increase sensitivity, but generally, the circuit configuration for self-excitation is complicated.
As a technique related to enhancement of detection sensitivity, Japanese Laid-open Patent Publication No. 2001-116783 discloses a method for detecting infinitesimal capacity change and a detection circuit which are for detecting an infinitesimal change in capacitance of a capacitor microphone. Also, Japanese Laid-open Patent Publication No. 2012-29972 discloses a technology for reducing real resistance components that increase due to occurrence of eddy current in a detection coil of a magnetic field detection device.